"In a series of executive orders, directives, and publicly released recommendations, the Trump Administration has proposed reorganizing the executive branch. The reorganization proposals range from restructuring entities within an existing agency, to moving entities from one existing agency to another, to consolidating existing agencies into newly created departments, to privatizing certain government agencies. The Administration has indicated that it considers some of these proposals to be within its existing authority, while others may require new legislation authorizing such action. These orders and proposals have prompted a recurring question concerning the composition of the federal government: who decides how to organize agencies and departments within the executive branch? The ultimate answer to this question is Congress. Legislative enactments create executive agencies and delegate authority to those entities to carry out various statutory functions and duties. But executive branch agencies also typically enjoy some discretion in determining how best to structure themselves to carry out their statutory responsibilities, provided that reorganization does not conflict with their governing statutes or legislative funding restrictions."
CRS Legal Sidebar, LSB10158
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html